In recent years, multiple functions of a mobile terminal device, such as a mobile phone, have been improved. A user may perform various operations while looking at a screen of a display device mounted on a mobile terminal device. There may be various input devices by which the user performs operations. For example, there is a mobile terminal mounting a scroll wheel to display a menu according to a scrolling operation of the scroll wheel (see, for example, Japanese Laid-open Patent Publication No. 2006-323820).
Furthermore, a touch panel may be used as a unit for operations performed by the user. For example, there is an on-vehicle information display device in which an image of a scroll dial is displayed on a monitor with a touch panel. When an edge part of the image of the scroll dial is touched, the on-vehicle information display device scrolls the menu displayed on the monitor (see, for example, Japanese Laid-open Patent Publication No. 2004-12919). Furthermore, there is a navigation device that displays a map and a trackball on a display screen with a touch panel. This navigation device scrolls the map according to a rubbing operation of the trackball on a displayed area (see, for example, Japanese Laid-open Patent Publication No. 2007-292834).
The techniques described in Japanese Laid-open Patent Publication No. 2004-12919 and Japanese Laid-open Patent Publication No. 2007-292834 enable the user to scroll the screen by touching an area in which an image for operations, such as an image of a scroll dial or a trackball, is displayed. However, since the image for operations is small and displayed at the edge of the display device, operability of a touch operation is low. This is a big problem specifically for a device, such as a mobile terminal device, in which the display area may not be large.